Membrane Bonding

ABSTRACT

Systems and techniques are provided for membrane bonding. A bonding agent may be applied to one or both of an ultrasonic device and membrane. The membrane may be placed on the ultrasonic device such that the membrane is in contact with the ultrasonic device through the bonding agent. The membrane and the ultrasonic device may be placed in between a first flat plate and a second flat plate, such that the second flat plate rests on top of the membrane. Light pressure may be applied to the membrane. The light pressure may be applied by one or more of the weight of the second flat plate and a pressure providing device applying pressure to either or both of the first flat plate and the second flat plate.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/164,108, filed on May 20, 2015.

BACKGROUND

Electromechanically active devices may be used in a variety ofapplications. For example, electromechanically active devices may beused in transducers, sensors, and, actuators. In some uses, theelectromechanically active device may be used to generate soundwaves,including ultrasonic sound waves, through vibration of theelectromechanically active device. A membrane, or diaphragm, may beadded to the electromechanically active device to provide additionalsurface area to move a medium, such as the air, with the vibrations ofthe electromechanically active device. The membrane may be tuned tooptimize various parameters of the performance of theelectromechanically active device, such as enabling efficient energytransfer between different media or tuning resonant performance of theelectromechanically active device to a specific frequency.

BRIEF SUMMARY

According to an implementation of the disclosed subject matter, abonding agent may be applied to one or both of an ultrasonic device andmembrane. The membrane may be placed on the ultrasonic device such thatthe membrane is in contact with the ultrasonic device through thebonding agent. The membrane and the ultrasonic device may be placed inbetween a first flat plate and a second flat plate, such that the secondflat plate rests on top of the membrane. Light pressure may be appliedto the membrane. The light pressure may be applied by one or more of theweight of the second flat plate and a pressure providing device applyingpressure to either or both of the first flat plate and the second flatplate.

A stencil may be placed on an ultrasonic device such that the stencilcovers one or more ultrasonic transducers of the ultrasonic device. Thestencil may include one or more openings. An epoxy may be applied to theultrasonic device through the one or more openings of the stencil. Theepoxy may form epoxy lines on the ultrasonic device. The epoxy may beapplied to electromechanically active devices of the ultrasonictransducers. The stencil may be removed from the ultrasonic device. Amembrane may be placed on the ultrasonic device such that the membraneis in contact with the epoxy. The membrane may cover one or more of theultrasonic transducers. The membrane and the ultrasonic device may beplaced between a first flat plate and a second flat plate, such that thesecond flat plate is in contact with the membrane and the first flatplate is in contact with the ultrasonic device opposite the second flatplate. Light pressure may be applied to the membrane or the ultrasonicdevice through either or both of the first flat plate and the secondflat plate for at least part of the curing time of the epoxy.

Systems and techniques disclosed herein may allow for membrane bonding.Additional features, advantages, and embodiments of the disclosedsubject matter may be set forth or apparent from consideration of thefollowing detailed description, drawings, and claims. Moreover, it is tobe understood that both the foregoing summary and the following detaileddescription are examples and are intended to provide further explanationwithout limiting the scope of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the disclosed subject matter, are incorporated in andconstitute a part of this specification. The drawings also illustrateembodiments of the disclosed subject matter and together with thedetailed description serve to explain the principles of embodiments ofthe disclosed subject matter. No attempt is made to show structuraldetails in more detail than may be necessary for a fundamentalunderstanding of the disclosed subject matter and various ways in whichit may be practiced.

FIG. 1 shows an example ultrasonic device according to an implementationof the disclosed subject matter

FIG. 2 shows an example stencil according to an implementation of thedisclosed subject matter.

FIG. 3 shows an example ultrasonic device according to an implementationof the disclosed subject matter.

FIG. 4 shows an example of an ultrasonic device according to animplementation of the disclosed subject matter.

FIG. 5 shows an example of membrane bonding according to animplementation of the disclosed subject matter.

FIG. 6 shows an example ultrasonic transducer cell according to animplementation of the disclosed subject matter.

FIG. 7 shows an example ultrasonic transducer cell according to animplementation of the disclosed subject matter.

FIG. 8 shows an example ultrasonic transducer cell according to animplementation of the disclosed subject matter.

FIG. 9A shows an example ultrasonic device according to animplementation of the disclosed subject matter.

FIG. 9B shows an example ultrasonic device according to animplementation of the disclosed subject matter.

FIG. 10 shows a process suitable for membrane bonding according to animplementation of the disclosed subject matter.

DETAILED DESCRIPTION

According to embodiments disclosed herein, membrane bonding may allowfor the bonding of a membrane to an electromechanically active device.

An ultrasonic device may include ultrasonic transducers on a substrate,such as on a Printed Circuit Board (PCB.) An ultrasonic transducer mayinclude an electromechanically active device, such as a cantilever orflexure, attached to the wall of a cavity in the substrate. A stencilmay be placed over the ultrasonic device. The stencil may be used toapply epoxy in a border around individual ultrasonic transducers and tothe tips of the electromechanically active devices. A membrane may beplaced on top of the ultrasonic device and pressed into the epoxy. Theultrasonic device, with the membrane, may be placed between flat plates,which may be used to apply light pressure to the ultrasonic device andmembrane. The ultrasonic device and membrane may be left under pressurefor the cure cycle of the epoxy. After the epoxy has cured, the membranemay be bonded to the ultrasonic device, with each ultrasonic transducerof the ultrasonic device being bonded to a separate section of themembrane. Bond lines of epoxy may separate the sections of the membrane,allowing them to move separately.

An ultrasonic device may include transducers on a substrate. Thesubstrate may be any suitable material, and may be, for example, a PCBwith any suitable number of layers. The substrate may be in any suitableshape, and the surface of the substrate may be flat, or may be curved ortextured in any suitable manner. A transducer of an ultrasonic devicemay include an electromechanically active device attached to a wall of acavity in the substrate. The electromechanically active device may be acantilever or flexure, and may be, for example, a piezoceramic unimorphor bimorph. The cavity may be any suitable shape and depth. For example,the cavity may be circular. The cavity may be created in the substratein any suitable manner, including through subtractive processes, such asdrilling, or additive processes. The electromechanically active devicemay be attached to the wall of the cavity in any suitable manner. Forexample, a step structure may be created on an edge of the cavity, andthe electromechanically active device may be bonded to the stepstructure using any suitable adhesive, such as, for example, conductiveepoxy. The electromechanically active device may be any suitable lengthand width for vibration at ultrasonic frequencies, and may be orientedin the cavity at any suitable angle. For example, theelectromechanically active device may reach approximately halfway acrossthe cavity. The top surface of the electromechanically active device,which may be, for example, a passive material of a unimorph or an activematerial of a bimorph, may be level, or near-level, with the top of thecavity. In some implementations, a transducer may include more than oneelectromechanically active device within a cavity. The ultrasonic devicemay include any number of ultrasonic transducers in any suitablearrangement.

A membrane may be bonded to the ultrasonic device to create anultrasonic device with a membrane. The membrane and electromechanicallyactive devices of an ultrasonic device may be cleaned using any suitablesolvents and acids. For example, acetone, methanol, isopropanol may beused to clean bonding surfaces of the electromechanically activedevices. Chromic acid, hydrochloric acid, and other suitable substancesor materials which may be promote adhesion may also be used to clean theelectromechanically active devices. The electromechanically activedevices may also be cleaned using an ultrasonic bath or plasma etching.The membrane may be cut larger than the area needed to cover theultrasonic device. The membrane may be any suitable material orcomposite material structure, which may be of any suitable stiffness andweight, for vibrating at ultrasonic frequencies. For example, themembrane may be both stiff and light. For example, the membrane may bealuminum shim stock, metal-patterned Kapton, or any other metal-patternfilm. The membrane may be impedance matched with the air to allow formore efficient air-coupling of the ultrasonic transducers. The membranemay include additional structures, such as, for example, ring structureslocated on the membrane where the membrane will contact the tips of theelectromechanically active devices. After being cut, the side of themembrane which will be bonded to the ultrasonic device, or bondingsurface, may have surface preparations applied to promote adhesion of anepoxy. These preparations may include plasma cleaning, chemical etching,mechanical texturing, or chemical activation. For example, the bondingsurface of the membrane may be textured using sandpaper, an abrasivecleaning pad, or an abrasive slurry. The bonding surface of the membranemay be cleaned using isopropanol.

An epoxy or other suitable bonding agent may be used to bond themembrane to the ultrasonic device. The membrane may be bonded to thesubstrate of the ultrasonic device, as well as to theelectromechanically active devices of the ultrasonic transducers. Theepoxy may be conductive or non-conductive. The epoxy may have a highviscosity while still being spreadable. The epoxy may have any suitablecuring schedule. For example, the epoxy may have a curing schedule thatmay allow the epoxy to cure while staying below 90 degrees Celsius. Thismay allow the epoxy to be cured without causing an electrically activematerial, such as a piezoceramic, of an electromechanically activedevice to reach its Curie temperature during the curing of the epoxy.The epoxy may cure within 48 hours. The epoxy may be mixed with glassmicrospheres whose diameter falls within a given range and that may havea target size. The diameters of the spheres may be narrowly distributedabout the target size. For example, if the target size is 100micrometers, then over 95% of the spheres may have diameters within afew percent of 100 micrometers. The glass microspheres may have anysuitable diameter, such as from 10 to 100 micrometers in diameter. Theglass microspheres may be used to determine the thickness, up from thesurface of the ultrasonic device, of the bond lines formed by the curedepoxy, as the bond may be as thick as the thickness of the glassmicrospheres. The glass microspheres may also allow the epoxy to formstandoffs between the tips, of the electromechanically active devicesand the membrane, separating them by more than just the thickness of theepoxy alone. The amount of glass microspheres mixed with the epoxy maybe high enough to allow proper distribution of the glass microspheresthroughout the epoxy and low enough to not alter the properties of thebond formed by the cured epoxy in any significant manner. When pressureis applied to the bond, the glass microspheres of a given diameter maystop the two sides from moving together so that the separation betweenthe sides is about equal to the given diameter of the microspheres.

The epoxy may be applied to the ultrasonic device. For example, theepoxy may be applied using screen printing techniques. A stencil may beplaced over the ultrasonic device. The stencil may be made of anysuitable material, including metal, such as stainless steel, orpolyimide, may be of any suitable thickness, for example, from 25micrometers to 100 micrometers thick, and may be patterned. For example,the stencil may be stainless steel that is 50 micrometers thick. Thepattern of the stencil may include openings or apertures, which may bein any suitable shapes, such as, for example, squares, circles, andhexagons. The pattern of the stencil may, for example, include an arrayof dashed squares with dots at the center. The dashed squares may bepatterned with any suitable number of dashes. For example, each dashedsquare may have two dashes per side, with sides shared by neighboringsquares. The size of the dashed squares may define the size of anultrasonic transducer cell of the ultrasonic device. The width of thedashes may affect the size of the ultrasonic transducers cells, and thearea of the section of the membrane that moves, and may be as thin aspossible in order to allow for larger ultrasonic transducer cells. Insome implementations, the stencil pattern may result in an ultrasonictransducer cell including more than one ultrasonic transducer. The dotsmay be positioned such that epoxy applied through the dots when thestencil is placed over the ultrasonic device may be deposited onto thetips of the free ends of the electromechanically active devices. Thestencil may be placed over the ultrasonic device using predrilledfiducials in both the stencil and the ultrasonic device to obtain properalignment. Epoxy may be spread over the stencil using a metal straightedge or non-compliant rubber squeegee, applying the epoxy to theultrasonic device through the openings in the stencil. For example, theepoxy may form squares, or dashed squares, around each ultrasonictransducer, with a dot of epoxy applied to the tip of the free end ofeach ultrasonic transducer's electromechanically active device. Thestencil may be removed after the epoxy has been applied.

The ultrasonic device, with applied epoxy, may be placed on a first flatplate, which may rest on or be attached to a surface. The first flatplate may be any suitable material, and any suitable thickness. Themembrane may be placed onto the ultrasonic device. The membrane may beplaced with the prepared bonding surface of the membrane coming intocontact with the epoxy on the ultrasonic device. A second flat plate maybe placed on top of the membrane, and may be used to apply lightpressure to the membrane and ultrasonic device, ensuring contact betweenthe membrane and the epoxy on the ultrasonic device. The light pressuremay be, for example, ¼ PSI or above while being below a pressure levelthat would crack the glass microspheres of the epoxy Pressure may beapplied in any suitable manner, including, for example, through theweight of the second flat plate on top of the membrane, or through apneumatic cylinder or other pressure providing device which may be usedto provide a controlled amount of sustained pressure to the second flatplate. The light pressure may be kept on the membrane for the durationof the cure cycle of the epoxy, or may be removed part way through thecure cycle. In some implementations, pressure may be provided by theweight of the first flat plate. For example, the membrane may be placedon top of the second flat plate, with the ultrasonic device on top ofthe membrane. The first flat plate may then be placed on top of theultrasonic device, with the weight of the first flat plate applyingpressure that may push the ultrasonic device towards the membrane. Thefirst flat plate may also be attached to a pressure providing deviceinstead of, or along with, the second flat plate.

When the cure cycle of the epoxy has completed, the ultrasonic devicewith attached membrane may be removed from between the flat plates. Themembrane may be attached to the ultrasonic device along bond linesformed by the cured epoxy. The bond lines may reflect the pattern of thestencil, for example, forming a grid and dividing the ultrasonic deviceinto square ultrasonic transducer cells. The membrane may also be bondedto the tips of the free end of each electromechanically active device ofthe ultrasonic device. This may result in each ultrasonic transducerbeing covered with a section of the membrane that is bonded to thesubstrate of the ultrasonic device around the ultrasonic transducer andalso bonded to the tip of the free end of the ultrasonic transducer'selectromechanically active device. The tip of the free end of theelectromechanically active device may be slightly off being aligned withthe center of the section of the membrane. This may allow the section ofthe membrane to be pushed outward by the electromechanically activedevice so that the highest point of the section of the membrane is atthe center of the section of the membrane. Each section of the membranemay be able to move independently of any other section of the membrane,though the membrane may remain a single piece of material. The bondlines formed by the cured epoxy may mechanically isolate the sections ofthe membrane from each other. The movement of one section of themembrane may not be transmitted across a bond line, where the membraneis bonded to the substrate, to another section of the membrane.

In some implementations, the epoxy or other suitable bonding agent maybe applied directly to the bonding surface of the membrane in additionto, or in lieu of, of the application of the epoxy or bonding agent tothe ultrasonic device. The epoxy or bonding agent may be applied to thebonding surface of the membrane using screen printing techniques and astencil. The stencil may include the same pattern as the stencil thatmay be used to apply epoxy or a bonding agent to the ultrasonic device,or may have a different, for example, complementary, pattern. Forexample, a stencil may be used to apply epoxy to the bonding surface ofthe membrane to form a grid pattern, while a second stencil may be usedto apply epoxy dots to the tips of the free ends of theelectromechanically active devices.

In some implementations, more than one membrane may bonded to anultrasonic device. For example, multiple separate membranes of the samematerial, or different materials may be used to cover the ultrasonictransducers of an ultrasonic device. Different materials may be used,for example, to allow different sections of the ultrasonic device tohave different operating characteristics.

FIG. 1 shows an example ultrasonic device according to an implementationof the disclosed subject matter. An ultrasonic device 100 may include asubstrate 160 and ultrasonic transducers 110. The ultrasonic transducers110 may include a main cavity 130, a secondary cavity 140, a channel150, and an electromechanically active device 120. The substrate 160 maybe any suitable substrate, such as, for example, a PCB, and may be inany suitable shape and of any suitable thickness. The substrate 160 mayinclude any number of fiducials, which may be, for example, predrilled.The first cavity 130 may be a cavity in the substrate 160, formedthrough any suitable additive or subtractive processes, and may be anysuitable shape and any suitable depth. For example, the cavity 160 maybe circular. The second cavity 140 may be a cavity in the substrate 160which may overlap the first cavity 130, and may any suitable shape andany suitable depth. For example, the second cavity 140 may be a circularcavity of less depth than the first cavity 130, forming a first stairstep at its intersection with the first cavity 130. The channel 150 maybe a channel of any suitable width and depth, made in any suitablemanner, which may run through the centers of the first cavity 130 andthe second cavity 140. For example, the channel 150 may be made using adicing saw cut of any suitable width through the first cavity 130 andthe second cavity 140. The channel 150 may be shallower than the secondcavity 150, so that the channel forms second stair step where itoverlaps the second cavity 150. The second stair step may be inalignment with the first stair step. The channel 150 may run across anumber of ultrasonic transducers 110, for example, if the ultrasonictransducers 110 are aligned on the substrate 660 so that a straight linecut from a dicing saw may pass through the centers of all of the firstcavities 130 and second cavities 140 in a group of aligned ultrasonictransducers 110.

The electromechanically active device 120 may be any suitableelectromechanically active device such as, for example, piezoelectricunimorph or bimorph which may use piezoceramic material bonded to anelectrically inactive substrate. The electromechanically active device120 may be any suitable shape, and may, be for example, a cantilever orflexure. The electromechanically active device 120 of the ultrasonictransducer 110 may be bonded to the substrate 160 at the first andsecond stair steps, with the free end of the electromechanically activedevice 120 projecting out over the bottom of the first cavity 130. Thefirst and second stair steps may also include electrodes connected tovias which may go into the substrate 160, and may be bonded toelectrodes of the electromechanically active device 120 using conductiveepoxy. The top surface of the electromechanically active device 120 maybe level with, or slightly below, the top surface of the substrate 160.

FIG. 2 shows an example stencil according to an implementation of thedisclosed subject matter. A stencil 200 may include any suitable patternof openings in any suitable shapes. The shapes may be, for example,squares, circles, rectangles, hexagons, octagons, other regularirregular polygons, or irregular shapes, and may be arranged in anysuitable pattern, including a square grid, hex grid, concentric circlesor other regular or irregular pattern. The stencil 200 may include anycombination of shapes in any combination of patterns. For example, thestencil 200 may include a dashed squared pattern including dashedsquares 210. The dashes 220 may be openings in the stencil, and may forma pattern of dashed squares 210 with shared sides. Any number of dashes220 may be used to form each side of the dashed squares 210 of thestencil 200. The center of each of the dashed squares 210 may include adot 230, which may be a circular opening in the stencil 200, or may beany other suitably shaped opening. The stencil 200 may have any suitablethickness, and may be, for example, between 25 micrometers and 100micrometers thick. The stencil 200 may be made from any suitablematerial, including metals and polyimides. For example, the stencil 200may be 50 micrometer thick stainless steel. The stencil 200 may includeany suitable number of fiducials, which may be, for example, predrilled,to allow for alignment of the stencil 200 with the ultrasonic device 100based on the fiducials of the substrate 160.

FIG. 3 shows an example ultrasonic device according to an implementationof the disclosed subject matter. The electromechanically active devices120 of the ultrasonic device 100 may be cleaned using solvents andacids. For example, acetone, methanol, and isopropanol may be used toclean the electromechanically active devices 120. Chromic acid,hydrochloric acid, and various other materials which may promoteadhesion may also be used.

The stencil 200 may be placed over the ultrasonic device 100. Thestencil 200 may be aligned with the ultrasonic device 100 so that thedots 230 are placed over the tips of the free ends of theelectromechanically active devices 120. Fiducials on the stencil 200 andthe substrate 160 may be used to obtain proper alignment of the stencil200 with the ultrasonic device 100. Epoxy may be applied to theultrasonic device 100 through the stencil 200 using screen printingtechniques. For example, epoxy may be applied through the openings inthe stencil 200, such as the dashes 200 and the dots 230, by using ametal straight-edge or non-compliant rubber squeegee to spread epoxyover the stencil 200. The epoxy may be any suitable epoxy or otherbonding agent, may be conductive or non-conductive, and may have a highviscosity while still being spreadable. The epoxy may having a curingschedule that allows the epoxy to cure at temperatures below 90 degreesCelsius, and to cure within 48 hours. The epoxy may be mixed with glassmicrospheres, which may between 10 micrometers and 100 micrometers indiameter. Enough glass microspheres may be used to allow the glassmicrospheres to be distributed throughout the epoxy withoutsignificantly impacting the properties of the bond formed by the curingthe epoxy.

After the epoxy is applied to the ultrasonic device 100, the stencil 200may be removed. The epoxy applied to the ultrasonic device 100 throughthe stencil 200 may form epoxy lines 320 and epoxy dots 330. The epoxylines 320 may form a pattern on the ultrasonic device 100 similar to thepattern of the stencil 200, for example, forming ultrasonic transducercells 310 which may be the same size as the dashed squares 210 of thestencil 200. The epoxy dots 330 may be located on the tips of the freeends of the electromechanically active devices 120.

In some implementations, the pattern of the stencil 200 may result indifferent numbers of ultrasonic transducers 110 being included within asingle ultrasonic transducer cell 310. For example, each ultrasonictransducer cell 310 may include only one ultrasonic transducer 110, ormay include two or more ultrasonic transducers 110.

FIG. 4 shows an example of an ultrasonic device according to animplementation of the disclosed subject matter. A membrane 400 may becut to an appropriate size for the ultrasonic device 100, for example,slightly larger than the area which the membrane 400 is intended tocover on the ultrasonic device 100. The membrane 400 may be any suitablelight and stiff material for vibrating at ultrasonic frequencies, suchas, for example, aluminum shim stock, metal-patterned Kapton, or anyother metal-patterned film. The membrane 400 may also include suitablepatterned structures. One surface of the membrane 400 may be the bondingsurface, and may be prepared for bonding using plasma cleaning, chemicaletching, mechanical texturing, or chemical activation. The bondingsurface of the membrane 400 may also be textured using sandpaper, anabrasive cleaning pad, or an abrasive slurry. The membrane may then becleaned, for example, with isopropanol.

The membrane 400 may be placed on the ultrasonic device 100 so that theprepared bonding surface of the membrane 400 contacts the epoxy on theultrasonic device 100. The membrane 400 may be aligned with theultrasonic device 100 so that it covers all of the epoxy, with the epoxynear the edges of the ultrasonic device 100 covered by the edges of themembrane 400. As the epoxy cures, the membrane 400 may be separated intomembrane sections 410 along bond lines 420, which may be the result ofcured epoxy lines 320.

FIG. 5 shows an example of membrane bonding according to animplementation of the disclosed subject matter. The ultrasonic device100 with the membrane 400 may be placed in between two flat plates 510and 520. The flat plates 510 and 520 may be made of any suitablematerial, and may be of any suitable thickness. Light pressure may beapplied to the membrane 400 through the flat plate 510 to ensure themembrane 400 remains in contact with the epoxy on the ultrasonic device100. The pressure may be applied through the weight of the flat plate510, or through some pressure providing device attached to the flatplate 510 or flat plate 520. Light pressure may be kept on the membrane400 for the entire curing cycle of the epoxy, or may be removed duringthe curing cycle. Once the curing cycle of the epoxy has completed, themembrane 400 may be bonded to the ultrasonic device along bond lines 420and at the locations of the epoxy dots 330, where theelectromechanically active devices 120 may be bonded to the membrane400. This may form membrane sections 410. The membrane sections 410 maybe mechanically isolated from each other by the bond lines 420, and maybe able to move independently even while the membrane 400 remains in onepiece. For example, when each membrane section 410 covers a singleultrasonic transducer 110, a membrane section 410 may be moved by theelectromechanically active device 120 of the ultrasonic transducer 110covered by the membrane section 410 without moving or disturbing anyother membrane section 410.

FIG. 6 shows an example ultrasonic transducer cell according to animplementation of the disclosed subject matter. The ultrasonictransducer cell 310 may include the ultrasonic transducer 110, includingthe substrate 160, the first cavity 130, the second cavity 140, thechannel 150, the electromechanically active device 120, and the membranesection 410.

FIG. 7 shows an example ultrasonic transducer cell according to animplementation of the disclosed subject matter. When the stencil 200 isused to apply epoxy to the ultrasonic device 100, the bond lines 320 maybe deposited around the ultrasonic transducer 110, creating the bordersof the ultrasonic transducer cell 310. The epoxy dot 330 may be locatedon the tip of the free end of the electromechanically active device 120,which may project out over the first cavity 130.

FIG. 8 shows an example ultrasonic transducer cell according to animplementation of the disclosed subject matter. After the membrane 400is placed on the ultrasonic device 100 and the epoxy is cured, themembrane section 410 may be bonded along bond lines 420 to the curedepoxy around the borders of the ultrasonic transducer cell 310. Themembrane section 410 may cover the ultrasonic transducer 110, and may bebonded to the electromechanically active device 120 by the epoxy dot330.

FIG. 9A shows an example ultrasonic device according to animplementation of the disclosed subject matter. Each membrane section410 of the membrane 400 may cover an ultrasonic transducer 110 of theultrasonic device 100. The bond lines 420 may mechanically isolate eachmembrane section 410 through attachment of the membrane 400 to thesubstrate 160 of the ultrasonic device 100. The membrane section 410 maybe held above the top surface of the electromechanically active device120 by the epoxy dot 330. The epoxy dot 330 may bond the tip of theelectromechanically active device 120 slightly off the center of themembrane section 410. The membrane section 410 may cross over thechannel 150, and may be bonded to the substrate 160 on either side ofthe channel 150.

FIG. 9B shows an example ultrasonic device according to animplementation of the disclosed subject matter. The membrane sections,such as membrane sections 410, 910, and 915, of the membrane 400 may bemechanically isolated from each other by the bond between the membrane400 and the substrate 160 along the bond lines 420. For example, whenthe electromechanically active device 120 is activated and flexesupward, the membrane section 410 may be pushed upwards at the locationof the epoxy dot 330. Because the epoxy dot 330 is slightly off center,the membrane section 410 may be pushed upwards at its center by theepoxy dot 330 and the flexed tip of the electromechanically activedevice 120. The bond lines 420 may mechanically isolate the membranesection 410 from neighboring membrane section 210, so that movement ofthe membrane section 410 due to movement of the electromechanicallyactive device 120 does not cause any movement or disturbance of themembrane section 910. Similarly, the electromechanically active device925 may be activated and flex upward, pushing up the membrane section915. The neighboring membrane section 910 may be mechanically isolatedfrom the membrane section 915 by the bond lines 420.

FIG. 10 shows a process suitable for membrane bonding according to animplementation of the disclosed subject matter. At 1000, an ultrasonicdevice may be cleaned. For example, the electromechanically activedevices 120 of the ultrasonic device 100 may be cleaned using anysuitable solvents. The solvents may be, for example, acetone, methanol,and isopropanol, or chromic acid, hydrochloric acid, or other materialsthat may promote adhesion.

At 1002, a surface of a membrane may be prepared for bonding. Forexample, a surface of the membrane 400 may be plasma cleaned, chemicallyetched, textured with sandpaper, an abrasive cleaning pad, or anabrasive slurry, and chemically activated with an adhesion promotor. Themembrane 400 may made of aluminum shim stock, metal-patterned Kapton,other metal-patterned film, or any other suitable light, stiff material.After a surface of the membrane 400 is roughened, the membrane 400 maybe cleaned, for example, with isopropanol.

At 1004, epoxy may be applied to the ultrasonic device. For example, thestencil 200 may be placed on the ultrasonic device 100, covering theultrasonic transducers 110. An epoxy, which may be conductive ornon-conductive, may be applied to the ultrasonic device 100 throughopenings or apertures in the stencil 200, such as the dashes 220 and thedots 230, using a metal straight edge or non-compliant rubber-backedsqueegee. The epoxy may be mixed with glass microspheres, which may bebetween 25 micrometers and 100 micrometers in diameter. The stencil 200may be patterned, for example, with dashed squares 210, and the epoxymay form the pattern of the stencil 200 on the ultrasonic device 100.The stencil 200 may be removed from the ultrasonic device 100 afterapplication of the epoxy. The epoxy lines 320 may divide the ultrasonicdevice 100 into ultrasonic transducer cells 310. Each ultrasonictransducer cell 310 may include any number of ultrasonic transducers110. For example, each ultrasonic transducer cell 310 may include asingle ultrasonic transducer 110. The ultrasonic transducer cells 310may have any suitable shapes, which may be determined by the pattern ofthe stencil 200.

At 1006, the roughened surface of the membrane may be placed on theepoxy on the ultrasonic device. For example, the roughened surface ofthe membrane 400 may be placed on the ultrasonic device 100 to be incontact with the epoxy. The membrane 400 may cover the ultrasonictransducers 110 of the ultrasonic device 100. In some implementations,the membrane 400 may cover only some of the ultrasonic transducers 110.

At 1008, the ultrasonic device with the membrane may be placed betweenflat plates. For example, the ultrasonic device 100 with the membrane400 may be placed between flat plates 510 and 520. The bottom of theultrasonic device 100 may be placed onto the flat plate 520, and theflat plate 510 may be placed on top of the membrane 400.

At 1010, light pressure may be applied to the membrane for the curingtime of the epoxy. For example, the weight of the flat plate 510 mayapply light pressure to the membrane 400, ensuring it remains in contactwith the epoxy on the ultrasonic device 100, or pressure may be appliedthrough the flat plate 510 using any suitable pressure providing device.The pressure may push the membrane 400 towards the ultrasonic device100. The light pressure may be applied for the curing time of the epoxy.The curing time may be, for example, less than 48 hours, and the curingtemperature may be less than 90 degrees Celsius. In someimplementations, the light pressure may be removed before the end of thecuring time. After the epoxy has cured, the membrane 400 may be bondedto the ultrasonic device 100 along bond lines 420 and at epoxy dots 330on the tips of the electromechanically active devices 120. The bondlines 420 may create borders for ultrasonic transducer cells 310, whichmay each be covered by a membrane section 410 that may be mechanicallyisolated from other membrane sections 410 while still being part of themembrane 400.

The foregoing description, for purpose of explanation, has beendescribed with reference to specific embodiments. However, theillustrative discussions above are not intended to be exhaustive or tolimit embodiments of the disclosed subject matter to the precise formsdisclosed. Many modifications and variations are possible in view of theabove teachings. The embodiments were chosen and described in order toexplain the principles of embodiments of the disclosed subject matterand their practical applications, to thereby enable others skilled inthe art to utilize those embodiments as well as various embodiments withvarious modifications as may be suited to the particular usecontemplated.

1. A method comprising: applying a bonding agent to one or both of anultrasonic device and membrane; placing the membrane on the ultrasonicdevice such that the membrane is in contact with the ultrasonic devicethrough the bonding agent; placing the membrane and the ultrasonicdevice in between a first flat plate and a second flat plate, such thatthe second flat plate rests on top of the membrane; and applying lightpressure to the membrane, wherein the light pressure is applied by oneor more of the weight of the second flat plate and a pressure providingdevice applying pressure to either or both of the first flat plate andthe second flat plate.
 2. The method of claim 1, wherein applying thebonding agent to the ultrasonic device comprises: placing a stencil onthe ultrasonic device; and applying the bonding agent to the ultrasonicdevice through one or more openings in the stencil.
 3. The method ofclaim 2, wherein the stencil is placed on the ultrasonic device based onfiducials of the stencil and fiducials of a substrate of the ultrasonicdevice.
 4. The method of claim 2, wherein the openings of the stencilcomprise dashes and dots, the dashes forming a grid of dashed squareswith a dot at the center of each dashed square in the grid of dashedsquares.
 5. The method of claim 2, wherein the bonding agent applied tothe ultrasonic device creates borders of ultrasonic transducer cells,and wherein a dot of the bonding agent is applied to the tips of thefree ends of electromechanically active devices of the ultrasonicdevice.
 6. The method of claim 2, wherein the bonding agent is appliedusing a metal straight-edge or a non-compliant rubber squeegee.
 7. Themethod of claim 1, wherein the bonding agent is an epoxy.
 8. The methodof claim 1, wherein the light pressure is applied for the entire curingtime of the bonding agent.
 9. The method of claim 1, wherein the bondingagent cures to form bond lines bonding the membrane to the ultrasonicdevice.
 10. The method of claim 9, wherein the bond lines divide themembrane into mechanically isolated membrane sections.
 11. The method ofclaim 10, wherein each of the membrane sections is bonded by the curedbonding agent to the tip of the free end of an electromechanicallyactive device covered by the membrane section.
 12. The method of claim11, wherein the electromechanically active device is bonded to themembrane section off the center of the membrane section.
 13. The methodof claim 1, further comprising keeping the membrane and ultrasonicdevice at a temperature below 90 degrees Celsius for the curing time ofthe bonding agent.
 14. The method of claim 1, further comprising, beforeplacing the membrane on the ultrasonic device, preparing or texturing atleast one surface of the membrane.
 15. The method of claim 1, whereinthe membrane comprises a metal or metal-patterned film
 16. The method ofclaim 1, wherein the bonding agent is mixed with glass microspheres. 17.The method of claim 1, wherein the ultrasonic device comprises one ormore ultrasonic transducers on a substrate.
 18. The method of claim 1,wherein each ultrasonic transducer comprises an electromechanicallyactive device attached to the substrate and partially projecting outover a cavity in the substrate.
 19. The method of claim 11, wherein theelectromechanically active device is a piezoelectric unimorph or apiezoelectric bimorph.
 20. A method comprising: placing a stencil on anultrasonic device such that the stencil covers one or more ultrasonictransducers of the ultrasonic device, the stencil comprising one or moreopenings; applying an epoxy to the ultrasonic device through the one ormore openings of the stencil, wherein the epoxy forms epoxy lines on theultrasonic device, and wherein is epoxy is applied toelectromechanically active devices of the ultrasonic transducers;removing the stencil from the ultrasonic device; placing a membrane onthe ultrasonic device such that the membrane is in contact with theepoxy, wherein the membrane covers one or more of the ultrasonictransducers; placing the membrane and the ultrasonic device between afirst flat plate and a second flat plate, such that the second flatplate is in contact with the membrane and the first flat plate is incontact with the ultrasonic device opposite the second flat plate; andapplying light pressure to the membrane or the ultrasonic device througheither or both of the first flat plate and the second flat plate for atleast part of the curing time of the epoxy.
 21. The method of claim 20,wherein the epoxy lines are based on a pattern of the openings of thestencil.
 22. The method of claim 20, wherein the epoxy lines form bondlines after the epoxy has cured.
 23. The method of claim 22, wherein thebond lines divide the ultrasonic device into one or more ultrasonictransducer cells, wherein each ultrasonic transducer cell comprises oneor more ultrasonic transducers.
 24. The method of claim 23, wherein eachof the ultrasonic transducer cells further comprises a membrane sectionof the membrane bonded to the borders of the ultrasonic transducer cellby the cured epoxy of the bond lines.
 25. The method of claim 24,wherein each membrane section is mechanically isolated from the othermembrane sections of the membrane by the bond lines.
 26. The method ofclaim 25, wherein an electromechanically active device of one of theultrasonic transducers moves the membrane section covering theultrasonic transducer without disturbing a neighboring membrane section.27. The method of claim 20, wherein at least one of the openings of thestencil is a dot, and wherein the dot is aligned with a tip of a freeend of an electromechanically active device when the stencil is placedon the ultrasonic device.
 28. The method of claim 27, wherein the epoxyapplied through the dot of the stencil forms an epoxy dot on the tip ofthe free end of the electromechanically active device, and wherein theepoxy dot bonds the electromechanically active device to the membranewhen the epoxy dot cures.
 29. The method of claim 28, wherein theelectromechanically active device is bonded to a membrane section of themembrane off the center of the membrane section.
 30. The method of claim20, further comprising before placing the membrane on the ultrasonicdevice, preparing or texturing at least one surface of the membrane, andwherein the at least one prepared or textured surface is placed incontact with the epoxy of the ultrasonic device when the membrane isplaced on the ultrasonic device.
 31. The method of claim 20, wherein themembrane and the ultrasonic device are kept at a temperature of lessthan 90 degrees Celsius for the curing time of the epoxy.
 32. The methodof claim 20, wherein the epoxy is mixed with glass microspheres.
 33. Themethod of claim 32, wherein the glass microspheres are between 10micrometers and 100 micrometers in diameter.